1. Field of the Invention
The invention relates to a device for the detection and processing of optical radiations.
2. Discussion of the Invention
Long-wavelength optical detectors (greater than or equal to 5 micrometres) fall into two large main groups of devices:
Photoelectric effect semiconductor detectors. PA1 Photothermic detectors. PA1 The energy level E.sub.1 is the trap level and E.sub.2 the conduction band for the extrinsic photoconductors. PA1 The energy level E.sub.1 is the valence band, and E.sub.2 the conduction band for the intrinsic photoconductors, photovoltaics etc . . . PA1 (E.sub.2 -E.sub.1) is the barrier height in a Schottky detector. PA1 1. of operating readily at ambient temperature or slightly cooled, at high wavelengths (for example, more than 3 .mu.m). PA1 2. for detectors, of providing a very high impedance, even at ambient temperature, which permits a high amplification and a utilization as detector at ambient temperature. PA1 3. of all being capable of being manufactured by the technology of semiconductors and thus exhibiting a possibility of integration into a semiconductor system.
In the first case, these detectors operate only at low temperature. In fact, the principle of operation of these devices is based on the generation of free carriers by optical transition between 2 energy levels E.sub.1 and E.sub.2. Depending upon the type of application:
If an electromagnetic wave permits a transition (E.sub.2 -E.sub.1) of low energy value (110 meV, for example), the phonons at ambient temperature will be of sufficiently high energy (25 mev) and sufficiently numerous to cause this transition. In other words, the dark current is very large in such a device at ambient temperature and the detectivity of the photodetector (like its impedance) is extremely low (D*.sup..about. 10.sup.6 cm. .sqroot.Hz/W)
In the second case, that is to say in photo-thermic detectors, the increase in the temperature due to the absorption of the electromagnetic wave leads to a variation of the dielectric constant of a pyroelectric material. In contrast to the first group of devices (photoelectric effect semiconductor detectors), these detectors operate at ambient temperature. As optical transitions between associated levels are not involved, the electrical conductivity of these materials does not change, and the impedance of the capacitive structures remains very large, permitting high amplifications.